mopidy.backend — Backend API

The backend API is the interface that must be implemented when you create a backend. If you are working on a frontend and need to access the backends, see the mopidy.core — Core API instead.

URIs and routing of requests to the backend

When Mopidy’s core layer is processing a client request, it routes the request to one or more appropriate backends based on the URIs of the objects the request touches on. The objects’ URIs are compared with the backends’ uri_schemes to select the relevant backends.

An often used pattern when implementing Mopidy backends is to create your own URI scheme which you use for all tracks, playlists, etc. related to your backend. In most cases the Mopidy URI is translated to an actual URI that GStreamer knows how to play right before playback. For example:

  • Spotify already has its own URI scheme (spotify:track:..., spotify:playlist:..., etc.) used throughout their applications, and thus Mopidy-Spotify simply uses the same URI scheme. Playback is handled by pushing raw audio data into a GStreamer appsrc element.
  • Mopidy-SoundCloud created it’s own URI scheme, after the model of Spotify, and use URIs of the following forms: soundcloud:search, soundcloud:user-..., soundcloud:exp-..., and soundcloud:set-.... Playback is handled by converting the custom soundcloud:.. URIs to http:// URIs immediately before they are passed on to GStreamer for playback.
  • Mopidy differentiates between file://... URIs handled by Mopidy-Stream and local:... URIs handled by Mopidy-Local. Mopidy-Stream can play file://... URIs pointing to tracks and playlists located anywhere on your system, but it doesn’t know a thing about the object before you play it. On the other hand, Mopidy-Local scans a predefined local/media_dir to build a meta data library of all known tracks. It is thus limited to playing tracks residing in the media library, but can provide additional features like directory browsing and search. In other words, we have two different ways of playing local music, handled by two different backends, and have thus created two different URI schemes to separate their handling. The local:... URIs are converted to file://... URIs immediately before they are passed on to GStreamer for playback.

If there isn’t an existing URI scheme that fits for your backend’s purpose, you should create your own, and name it after your extension’s ext_name. Care should be taken not to conflict with already in use URI schemes. It is also recommended to design the format such that tracks, playlists and other entities can be distinguished easily.

Backend class

class mopidy.backend.Backend[source]

Backend API

If the backend has problems during initialization it should raise mopidy.exceptions.BackendError with a descriptive error message. This will make Mopidy print the error message and exit so that the user can fix the issue.

Parameters:
audio = None

Actor proxy to an instance of mopidy.audio.Audio.

Should be passed to the backend constructor as the kwarg audio, which will then set this field.

library = None

The library provider. An instance of LibraryProvider, or None if the backend doesn’t provide a library.

ping()[source]

Called to check if the actor is still alive.

playback = None

The playback provider. An instance of PlaybackProvider, or None if the backend doesn’t provide playback.

playlists = None

The playlists provider. An instance of PlaylistsProvider, or class:None if the backend doesn’t provide playlists.

uri_schemes = []

List of URI schemes this backend can handle.

Playback provider

class mopidy.backend.PlaybackProvider(audio, backend)[source]
Parameters:
change_track(track)[source]

Swith to provided track.

MAY be reimplemented by subclass.

It is unlikely it makes sense for any backends to override this. For most practical purposes it should be considered an internal call between backends and core that backend authors should not touch.

The default implementation will call translate_uri() which is what you want to implement.

Parameters:track (mopidy.models.Track) – the track to play
Return type:True if successful, else False
get_time_position()[source]

Get the current time position in milliseconds.

MAY be reimplemented by subclass.

Return type:int
pause()[source]

Pause playback.

MAY be reimplemented by subclass.

Return type:True if successful, else False
play()[source]

Start playback.

MAY be reimplemented by subclass.

Return type:True if successful, else False
prepare_change()[source]

Indicate that an URI change is about to happen.

MAY be reimplemented by subclass.

It is extremely unlikely it makes sense for any backends to override this. For most practical purposes it should be considered an internal call between backends and core that backend authors should not touch.

resume()[source]

Resume playback at the same time position playback was paused.

MAY be reimplemented by subclass.

Return type:True if successful, else False
seek(time_position)[source]

Seek to a given time position.

MAY be reimplemented by subclass.

Parameters:time_position (int) – time position in milliseconds
Return type:True if successful, else False
stop()[source]

Stop playback.

MAY be reimplemented by subclass.

Should not be used for tracking if tracks have been played or when we are done playing them.

Return type:True if successful, else False
translate_uri(uri)[source]

Convert custom URI scheme to real playable URI.

MAY be reimplemented by subclass.

This is very likely the only thing you need to override as a backend author. Typically this is where you convert any Mopidy specific URI to a real URI and then return it. If you can’t convert the URI just return None.

Parameters:uri (string) – the URI to translate
Return type:string or None if the URI could not be translated

Playlists provider

class mopidy.backend.PlaylistsProvider(backend)[source]

A playlist provider exposes a collection of playlists, methods to create/change/delete playlists in this collection, and lookup of any playlist the backend knows about.

Parameters:backend (mopidy.backend.Backend instance) – backend the controller is a part of
as_list()[source]

Get a list of the currently available playlists.

Returns a list of Ref objects referring to the playlists. In other words, no information about the playlists’ content is given.

Return type:list of mopidy.models.Ref

New in version 1.0.

create(name)[source]

Create a new empty playlist with the given name.

Returns a new playlist with the given name and an URI, or None on failure.

MUST be implemented by subclass.

Parameters:name (string) – name of the new playlist
Return type:mopidy.models.Playlist or None
delete(uri)[source]

Delete playlist identified by the URI.

MUST be implemented by subclass.

Parameters:uri (string) – URI of the playlist to delete
get_items(uri)[source]

Get the items in a playlist specified by uri.

Returns a list of Ref objects referring to the playlist’s items.

If a playlist with the given uri doesn’t exist, it returns None.

Return type:list of mopidy.models.Ref, or None

New in version 1.0.

lookup(uri)[source]

Lookup playlist with given URI in both the set of playlists and in any other playlist source.

Returns the playlists or None if not found.

MUST be implemented by subclass.

Parameters:uri (string) – playlist URI
Return type:mopidy.models.Playlist or None
refresh()[source]

Refresh the playlists in playlists.

MUST be implemented by subclass.

save(playlist)[source]

Save the given playlist.

The playlist must have an uri attribute set. To create a new playlist with an URI, use create().

Returns the saved playlist or None on failure.

MUST be implemented by subclass.

Parameters:playlist (mopidy.models.Playlist) – the playlist to save
Return type:mopidy.models.Playlist or None

Library provider

class mopidy.backend.LibraryProvider(backend)[source]
Parameters:backend (mopidy.backend.Backend) – backend the controller is a part of
browse(uri)[source]

See mopidy.core.LibraryController.browse().

If you implement this method, make sure to also set root_directory.

MAY be implemented by subclass.

get_distinct(field, query=None)[source]

See mopidy.core.LibraryController.get_distinct().

MAY be implemented by subclass.

Default implementation will simply return an empty set.

Note that backends should always return an empty set for unexpected field types.

get_images(uris)[source]

See mopidy.core.LibraryController.get_images().

MAY be implemented by subclass.

Default implementation will simply call lookup and try and use the album art for any tracks returned. Most extensions should replace this with something smarter or simply return an empty dictionary.

lookup(uri)[source]

See mopidy.core.LibraryController.lookup().

MUST be implemented by subclass.

refresh(uri=None)[source]

See mopidy.core.LibraryController.refresh().

MAY be implemented by subclass.

root_directory = None

mopidy.models.Ref.directory instance with a URI and name set representing the root of this library’s browse tree. URIs must use one of the schemes supported by the backend, and name should be set to a human friendly value.

MUST be set by any class that implements LibraryProvider.browse().

search(query=None, uris=None, exact=False)[source]

See mopidy.core.LibraryController.search().

MAY be implemented by subclass.

New in version 1.0: The exact param which replaces the old find_exact.

Backend listener

class mopidy.backend.BackendListener[source]

Marker interface for recipients of events sent by the backend actors.

Any Pykka actor that mixes in this class will receive calls to the methods defined here when the corresponding events happen in a backend actor. This interface is used both for looking up what actors to notify of the events, and for providing default implementations for those listeners that are not interested in all events.

Normally, only the Core actor should mix in this class.

playlists_loaded()[source]

Called when playlists are loaded or refreshed.

MAY be implemented by actor.

static send(event, **kwargs)[source]

Helper to allow calling of backend listener events

Backend implementations

See Backend extensions.